Effective reduction of undesirable internal combustion engine emissions, such as hydrocarbon, carbon monoxide, and oxides of nitrogen is provided through catalytic treatment of engine exhaust gas. Efficient catalytic treatment may be provided by passing engine exhaust gas through a catalytic converter which becomes catalytically active when heated, such as through heat energy transfer from engine exhaust gas, to light-off temperature, typically about 400 degrees Celsius.
It is known to apply supplemental heating to the converter or to the exhaust gas entering the converter to reduce the time to light-off following an engine coldstart. Electrical heating elements have been used as supplemental converter heaters in which a catalyzed electrical heating element is located close to or is integral with a low mass highly catalyzed surface to rapidly heat the element and surface to light-off. The element and surface are located upstream of the catalytic converter in the engine exhaust gas path. Once the element and the surface reach light-off temperature, engine exhaust gas products combined with a supply of oxygen will oxidize when passing thereby, releasing significant amounts of energy, which are passed to the catalytic converter and rapidly elevate the temperature thereof to light-off. Indeed, the energy released through this exothermic reaction rapidly increases to levels overwhelming the level of heat energy released by the electrical heating element. Accordingly, the element may be turned off shortly after the catalyst reaches light-off without materially affecting the time to light-off of the converter itself.
Over time, the catalyzed surface may tend to deteriorate in performance. Carbon passing through the engine exhaust gas path may impact the surface, disturbing the catalyst that is disposed thereon. Engine oil contaminants, such as phosphorus and zinc, may poison the catalyst, reducing its efficiency. It is difficult to predict the rate of deterioration in performance of the catalyst on the surface, as the behavior of the phenomena causing the deterioration is often not predictable. For example, the frequency that carbon particles impact the catalyzed surface is difficult to predict. Furthermore, the effect that any such impact may have on performance of the catalyst is extremely difficult to estimate.
What is known is that when such deterioration occurs, electrical power required for proper catalytic converter pre-heating will increase. For example, more power may be required to rapidly heat the catalyzed surface to light-off. In more advanced cases of catalyzed surface deterioration, the heating element may play a significant role in directly heating the catalytic converter itself--dramatically increasing its power requirement.
The significant power required to drive the electrical heating element of an electrically heated catalytic converter EHC significantly impacts the electrical system of the vehicle to which it is applied. Vehicle power supply limitations make it desirable to limit the power supplied to the electrical heating element of the EHC to the minimum power needed to elevate the converter to light-off in a desired time. This minimum power may be initially small for an undamaged catalyzed surface, but may increase substantially and unpredictably as the surface deteriorates.
Accordingly, it would be desirable to accurately estimate the minimum power needed to rapidly elevate the temperature of a catalytic converter to light-off in an EHC system, and to control the power provided the EHC in response to the estimation to minimize EHC power requirements while preserving the emissions benefit of the EHC.